I’m not sure what a “high end” surge protector may be, but if it wasn’t designed specifically for computer electronics, its thresholds may be to high and/or its attack times to slow to effectively protect computer electronics.
The filesystem of any computer may also get corrupted when there is a sudden power loss. As Roon OS is a closed system, I don’t know how good it may deal with such a situation. While there are many similar posts like yours, I never saw Roon Labs comment on the actual failure/failing device/part. So it can be a fried power supply, a damaged motherboard, a corrupted filesystem or a failing boot drive (during runtime, there is probably not much need to read data from this drive so some failure types might be unnoticed until the next restart {attempt}).
As you offered a short power outage as reason/starting point for your current issue, I just offered to think about adding a device (UPS) specifically designed to deal with such a situation. I don’t see this as blaming the user and given the uncertainty about the actual failure, even if you had one it might only have delayed the appearance of the issue until a later time – or it could also have totally saved you from all your current trouble (and is still much cheaper than a new Nucleus).